Conventional methods for obtaining random numbers include a method in which pseudo random numbers are employed and a method in which natural random numbers are employed. The pseudo random numbers are obtained by generating random numbers using a predetermined program while natural random numbers are obtained by generating random numbers utilizing a probability event that occurs in nature. The probability event (a seed of natural random numbers) that can be used includes, for example, thermal noise (Johnson noise) in a resistor. The obtained thermal noise is amplified and compared with a predetermined threshold to obtain binarized random numbers.
Methods that have been proposed as providing a seed of natural random numbers having larger amplitudes include a method in which noise in tunnel junctions (a sum of thermal noise and shot noise) is used [see, for example, Patent Reference 1 (a random number generating circuit using thermal noise in a tunneling device)], a method in which thermal noise is amplified by a single electron transistor effect [see, for example, Patent Reference 2 (a random number generating device using single electron tunneling phenomenon); Non-Patent Reference 1 (experiments on trap and release of electrons in an ultrathin film SOI (silicon-on-insulator) transistor], and a method in which thermal noise is amplified by two negative resistive elements [see, for example, Patent Reference 3 (a random number generating circuit using a negative resistive element such as Esaki diode)].
Patent Reference 1: Japanese Patent Laid-open Publication No. 2003-108364
Patent Reference 2: Japanese Patent Laid-open Publication No. 2004-030071
Patent Reference 3: Japanese Patent Laid-open Publication No. 2005-018500
Non-Patent Reference 1: K. Uchida et al., “Silicon single electron tunneling device fabricated in an undulated ultrathin silicon-on-insulator film,” J. Appl. Phys. No. 90 (2001), pp. 3551
Non-Patent Reference 2: R. Ohba et al., “Si Nanocrystal MOSFET with Silicon Nitride Tunnel insulator for High-rate Random Number Generator,” IEEE Computer Society Annual Symposium on VLSI2006
Non-Patent Reference 3: M. Pakala et al., “Critical current distribution in spin-transfer-switched magnetic tunnel junctions,” J. Appl. Phys. No. 98 (2005), pp. 056107K
Non-Patent Reference 4: [1] S. Yuasa et al., “Giant room-temperature magnetoresistance in single crystal Fe/MgO/Fe magnetic tunnel junctions,” Nature Material No. 3 (2004), pp. 868. [2] S. S. Parkin et al., “Giant tunneling magnetoresistance at room temperature with MgO(100) tunnel barrier,” Nature Material No. 3 (2004), pp. 862
Non-Patent Reference 5: A. A. Tulapurkar et al., “Subnanosecond magnetization inversion in magnetic nanopillars by spin angular momentum transfer,” Appl. Phys. Lett. No. 85 (2004), pp. 5358.